Waste disposal units such as used in the kitchen are usually driven by an electric motor, which rotates one or two stage cutters at high speed with considerable noise. In addition to requiring electrical wiring, there is the hazard of having electrical connections and equipment near water. If the cutters are jammed by an obstruction, such as a bone or other hard object, the motor is stalled and may be damaged. If an overload switch is installed this must be reset, and is often not very accessible. With the type of cutters normally used it is possible for fairly large particles to pass through and the accumulation in a pipe bend can cause ultimate blockage of the drain, particularly if insufficient flush water is used.
Water driven units have been developed but have had limited cutter action and are prone to jamming. A typical example is disclosed in U.S. Pat. No. 3,700,178, which has a reversing valve actuated by the piston at each end of the stroke, so that the mechanism can be jammed in a partial stroke position.